Global Occurrence and Environmental Fate of Microplastics in Stormwater Runoff: Unlock the In-depth Knowledge on Nature-Based Removal Strategies

Microplastics (MPs), defined as plastic particles smaller than 5 mm, originate from the degradation of larger plastic items or manufactured products, such as microbeads. Stormwater runoff is increasingly recognized as a critical pathway for introducing MPs into marine environments, thereby threatening both ecosystems and human health. Despite growing concerns over MPs as emerging contaminants, a significant knowledge gap remains regarding their global distribution and the associated challenges to human health. This highlights the need for comprehensive research into the factors influencing MP contamination in stormwater runoff. To collect data, the search was restricted to academic articles published between 2020 and 2024. After careful screening, 45 reports were selected and included in the current study. The sizes and global levels of MPs in stormwater runoff vary widely, with dominant particles being less than 1000 µm and concentrations ranging from as low as 1.2–3 particles/L to as high as 11,932 ± 151 to 18,966 ± 191 particles/L. Common MPs identified in stormwater include fragments, fibers, foams, films, rubbery particles, and spheres. The research findings underscore stormwater runoff as a significant pathway for transporting MPs within urban settings. Therefore, it is essential to prioritize treatment strategies specifically designed to remove MPs effectively. This necessitates adopting nature-based solutions like bioretention cells, rain gardens, sustainable urban drainage systems (SUDS), and constructed wetlands. Such strategies harness the inherent capabilities of natural ecosystems to efficiently filter and capture MPs, thereby significantly reducing pollution from stormwater runoff.